Method and apparatus for writing information into plated wire magnetic film memories



Nov. 11, 1969 ETSUO KASHIWAGI ETAL 3,478,336 METHOD AND APPARATUS FORWRITING INFORMATION INTO PLATED WIRE MAGNETIC FILM MEMORIES Filed Aug.16. 1966 2 Sheets-Sheet 1 QEE.Z

Wwm I a/J5 4101 4/42) Pd! :5

a" //VFO/?M4770/V 8\ 194 70 AX/J' 0/ Ml NET/Z4 770/) E5. 34 I 45) A): a;I M/Ig /VET/ZAT/WV A 0 (7 mmvroas. 7500 [FISH/W467 BY H/AO-Sl/AIMPIKQAI/ m4, %,dzln

NOV. 11, 1969 ETSUQ s -uw s ETAL 3,478,336

METHOD AND APPARATUS FOR WRITING INFORMATION INTO PLATED WIRE MAGNETICFILM MEMORIES Filed Aug. 16. 1966 2 Sheets-Sheet 2 I N VEN TORS 7500A4S///WI6/ By ,v/zasl/ Ara/24mm (M .44, M i J ATTOR/VE YS United StatesPatent Filed Aug. 16, 1966, Ser. No. 572,722 Claims priority,application Japan, Aug. 31, 1965, 40/ 53,194 Int. Cl. G11b 5/74 US. Cl.340-174 5 Claims ABSTRACT OF THE DISCLOSURE A memory system employingcylindrical shaped mem ory elements comprised of a rod-shaped conductorhaving a ferromagnetic coating upon its outer surface. A single turnwinding is disposed about the cylindrical shaped memory element. Pulsesof opposite polarity are applied to the winding and substantiallysimultaneously therewith an information pulse is applied to the rodshaped conductor timed so as to be initiated prior to the termination ofthe first pulse applied to the Winding and so as to terminate subsequentto the second pulse of opposite polarity applied to the winding so as toenable a reduction in the level of information current amplitudeutilized to drive such elements while maintaining suitable margins ofoperation.

The instant invention relates generally to writing methods and apparatusfor cylindrical magnetic film memories, and more particularly to a newand improved writing method and apparatus for such memories which iscapable of substantially increasing the allowable margin informationpulse amplitudes; that is, lowering the magnitude or level of theminimum input information pulse amplitude, and accordingly, enhancingthe reliability of cylindrical magnetic film memory elements which arepresently produced through the use of conventional manufacturingtechniques.

Whereas the description set forth in the instant specification isprimarily concerned with a novel writing or driving method for platedwire memory elements, it should be obvious to one having ordinary skillin the technology involved here that the new writing method andapparatus is equally applicable to the planar magnetic film memoryelements. Therefore, the description set forth herein should beconstrued to be of suflicient breadth as to encompass both types ofmemory elements or memory devices as a matter of course, while nospecific mention is made of planar film magnetic memory elements.

Whereas it is not difiicult to provide usable magnetic properties inmagnetic film memories produced in accordance with conventionaltechnological developments in individual cylindrical film memoryelements (when considering allowable limits for the word pulse or theinformation pulse magnitudes), the technique for quantity production ofmemory elements having substantially uniform magnetic characteristics athigh yield rates has still remained to be resolved as a most difiicultproblem confronting present-day technology.

Various technical suggestions have been proposed, and some have beenreduced to practice in the technological field of plated wire magneticfilm memories in order to effectively utilize individual memory elementsin magnetic film memory devices irrespective of the presence ofconsiderably non-uniform magnetic characteristics among the devicesproduced and thereby for enhancing the operational reliability of suchplated wire memory devices.

The principal objective of the instant invention is to provide asolution to this problem through the employment of a new and improveddriving or writing method and apparatus capable of greatly increasingthe usable margins of both word and information pulse amplitudes orcutting down the level of the minimum information current amplitudewhich may be used in driving magnetic film memory elements.

The writing method and apparatus according to the instant invention maybe employed in any memory plane comprised of a plurality of memoryelements, each of which includes a conducting substrate wire forconducting an information current pulse, a cylindrical magnetic filmcontinuously electroplated on the conducting substrate wire and havingan easy axis of magnetization in the circumferential direction; and aword line disposed substantially perpendicularly to the substrate wirefor the purpose of conducting a word current pulse.

An outstanding feature of the writing method of the instant inventionover conventional techniques is that the binary information states ONEand ZERO are written into the cylindrical magnetic film by introducingthe information current pulse before the cessation of the word pulseand, for some time after the cessation of the word pulse, and furtherintroducing an auxiliary word pulse opposite in polarity to the regularword pulse in the word line in the time interval between the cessationof the regular word pulse and that of the information pulse.

This write-in method causes a reversal of substantially all those atomsmagnetized in the binary ZERO (or binary ONE) state to reverse to thebinary ONE (or binary ZERO) state which constitutes a significantlygreater reversal from the viewpoint of the number of atoms reversed thanthat which occurs during conventional write-in operation.

It is, therefore, one object of the instant invention to provide a novelwrite-in method for cylindrical and planar film magnetic memory devicesin which an initial and an auxiliary current pulse are introduced intothe word pulse line during the write-in operation.

Another object of the instant invention is to provide a novel write-inmethod for cylindrical and planar film magnetic memory devices in whichan initial and an auxiliary current pulse are introduced into the wordpulse line during the write-in operation wherein the timingrelationships between the current pulses introduced into the word lineand the information current pulse introduced into the substrate wire aresuch that the information pulse is introduced before the cessation ofthe first word pulse and subsists for some time after the cessation ofthe word pulse, and wherein the auxiliary word pulse is opposite inpolarity to the first word pulse and occurs in the time interval betweenthe cessation of the first word pulse and the cessation of theinformation pulse.

These and other objects of the instant invention will become apparentwhen reading the accompanying description and drawings, in which:

FIGURE 1 is a perspective view showing a conventional cylindrical filmmemory element which may be employed with the novel method of theinstant invention.

FIGURE 2 is a waveform diagram showing typical current pulse waveformsand illustrating the time relationship among various pulses to beconducted in the memory element of FIGURE 1 in accordance with thewriting method of the instant invention.

FIGURES 3a, 3b and 30, respectively, are polar coordinate diagramspresented to facilitate an understand of the principles of thisinvention.

FIGURE 4 is a plot of curves derived from experimental data obtainedthrough the use of a cylindrical magnetic film memory, typicallyreferred to as a plated wire memory, in order to illustrate theadvantages of the the writing method of the instant invention ascompared with conventional writing methods.

FIGURE 1 shows a perspective view of the components employed in aconventional cylindrical magnetic film memory element which may beutilized with the writing method of the instant invention. Thearrangement of FIGURE 1 is comprised of a conducting substrate wire 1formed preferably of either copper or phosphorbronze. The magnetic film2 is continuously electroplated on the wire circumferential surface. Aword line 3, in the from of a single-turn solenoid, is disposed aroundsubstrate wire 1 so as to be aligned substantially perpendicular to wire1.

In the arrangement of FIGURE 1, the easy and hard axes of magnetizationof magnetic film 2 are respectively formed in the circumferential 2a andaxial 2b directions of substrate wire 1.

With this arrangement, a uniaxial magnetic anisotropy is introduced intothe magnetic film 2 to result in the two directions of magnetization,either clockwise or counterclockwise around the wire circumference. Thetwo magnetization directions are used to represent binary informationstates wherein a binary ONE state is chosen as the clockwise directionand the binary ZERO state as the counterclockwise direction, or viceversa, depending only upon the choice of the user.

FIGURE 2 shows typical current pulse waveforms which illustrate theconcept of the writing method according to the instant invention. It isconventional, in the field of plated wire memory elements, to read outbinary information which has been written into the magnetic film at theleading edge 4a of a word pulse current which is introduced into wordline 3 and to write binary information therein by introducing aninformation pulse 6 (or 6) in the conducting substrate wire 1 whichcorresponds to a binray ZERO (or binary ONE) in such a manner that theleading edge 6a (or 6a) of the information pulse is initiated before thecessation of the word pulse 4 and which sustains for a time intervalafter the cessation of the word pulse 4.

The writing method of the instant invention differs from theconventional writing method in that an auxiliary word pulse 5, as shownin FIGURE 2, is provided in addition to the ordinary word pulse 4. Theauxiliary word pulse 5 is opposite in polarity to the regular word pulse4, and the auxiliary word pulse 5 is introduced in the time intervalbetween the cessation of both the regular word pulse 4 and theinformation pulse 6 (or 6) for the purpose of lowering the allowableminimum information pulse amplitude of the information pulse current 6(or 6') introduced into the conducting substrate wire 1.

Although the auxiliary word pulse 5 and the regular word pulse 4 areshown as having substantially the same amplitudes, this illustration issimply by way of example, and, it should be understood, that the equalamplitude pulse relationship is by no means a necessary condition forproducing a successful writing operation according to this invention.

FIGURE 3a is a plot showing a polar coordinate system which serves as anaid toward understanding the principles of the writing method accordingto this invention. Such polar coordinates are also depicted in the formof similar graphs shown in FIGURES 3b and 30, to be more fullydescribed.

FIGURE 311 represents the magnetization state of a memory region in thecylindrical magnetic film possessing an anisotropic dispersion andassumes a binary ONE (or binary ZERO) has been perfectly written in themagnetic film 2.

Considering FIGURE 3a, the mean easy and hard axes of magnetization arerespectively in alignment with the ordinate and abscissa of the FIGURE3a plot. Stated more particularly, the loop 9 defines an area whichrepresents a density function indicative of the normalized ratio ofNi-Fe alloy atoms (forming the magnetic film) which have an easy axis ofmagnetization in a direction aligned at an angle 19 with the mean easyaxis of magnetization 7 relative to the total Ni-Fe alloy atoms asdepicted by the radius vector 10. The reference numeral 8 denotes thehard axis of magnetization. It can be seen to be obvious that this graphillustrates the case in which the mean easy and hard axes ofmagnetization coincide respectively with the circumferential and axialdirections 2a and 2b of magnetic film 2.

Incidentally, it is well known that the switching threshold regardingthe writing operation, or the amplitude relationship between the wordand information pulses employed in the writing operation normally followan astroid curve.

The polar diagram shown in FIGURE 3b illustrates the magnetizationreversal state of the memory region in the magnetization state asexpressed by loop 9 in FIGURE 3a which is obtained by a writingoperation (according to the conventional method) wherein a binary ZERO(or binary ONE) is written into the region of the magnetic film usingthe resultant magnetic field 11 in the filmthat is, by introducing aword pulse into word line 3 and an information pulse into the conductingsubstrate wire 1 having an amplitude which is less than the minimumvalue necessary for perfectly writing a binary ZERO (or binary ONE) inthe memory region. This imperfect writing operation results in the meaneasy and hard axes of magnetization being aligned at an angle relativeto the perfect mean easy and hard axes of magnetization.

Of the two loops shown in FIGURE 3b, the loop 12 defines an areacorresponding to the number of atoms for which the magnetizationreversal has occurred, whereas the area defined by loop 13 represents anarea corresponding to the remaining number of atoms for which nomagnetization reversal has occurred. It can clearly be seen from aconsideration of FIGURE 2b that a substantial number of atoms fail toundergo a magnetization reversal.

FIGURE 30 illustrates the magnetization reversal state for the samememory region considered in conjunction with the polar diagrams ofFIGURES 3a and 3b and which is obtained by the novel writing methoddescribed herein. The graph of FIGURE 30 may best be understood byanalyzing the writing operation which may be divided into two successiveoperations as follows:

The first operation constitutes the magnetization reversal stateoccurring under control of a write-in operation as the result of themagnetic field 11 in the magnetic film which is produced by a word pulse4 and an information pulse having the same amplitude as that ofinformation pulse 6 which has been referred to in explaining the polardiagram of FIGURE 3b. This operation results in the polar diagram ofFIGURE 3b.

Now, considering the writing operation as including the additionaloperation of producing a resultant magnetic fluid 14 generated by theauxiliary word pulse 5 and the above mentioned information pulse 6, itis found that magnetization reversal also occurs, as shown by the loopdefining area 13' which includes the atoms corresponding to area 13 inpolar diagram FIGURE 3b that have failed to perform the magnetizationreversal in the process employed in FIGURE 3b.

From the foregoing description, it can be readily understood that themargin of the information current pulse for the magnetic film can begreatly increased, and the write-in characteristics of the memoryelement can be greatly improved when employing the principles of theinstant invention.

If rotational vector diagrams similar to those shown in FIGURE 3 wereconsidered, it would not be difficult to conclude that the allowablerange of information current can be greatly increased, and this effectaccomplished when a binary ONE (or binary ZERO) is written into themagnetic film, provided that the magnetic film possesses a skew (thatis, where the direction of the hard axis of magnetization of the filmdeviates from the axial direction of the substrate wire by some angle),in the case where the magnetic film does not possess an anisotropydispersion.

FIGURE 4 is a plot showing experimental data which was compiled usingthe memory plane employing the memory element components of FIGURE inorder to show a comparison between the conventiona and the improvedwriting methods.

Each of the memory elements in the memory plane consisted of a substratewire 1 having a diameter of 0.20 mm. with a magnetic film electroplatedthereon having a thickness of 1 micron. A three-turn solenoid-type wordline was disposed around the plated Wire so as to be alignedsubstantially perpendicular to substrate 1. The solenoid-type word lineshad a diameter of 0.10 mm. and the solenoidtype word lines were providedwith a suitable insulation. The memory plane was arranged with aplurality of substrate wires 1 being disposed in spaced parallel fashionso that on-center distances between substrate wires were 1.50 mm. Aplurality of word lines were disposed in spaced parallel fashion so thattheir on-center distances were 2.0 mm. The coercive force, the uniaxialanisotropy field strength, and the dispersion angle of the film wererespectively 1.7 oersteds, 2.6 oersteds, and approximately 2 degrees.

In FIGURE 4, readout signal level and information pulse amplitudes arerespectively plotted along the ordinate 16 and the abscissa 15.

Curve 17 is a plot relating the relationship between readout signallevel and information pulse amplitude of a memory elements after it hasbeen subjected to the following process:

CASE NO. 1

A binary ZERO was written once into the magnetic film by use of theconventional writing method subsequent to the time in which a binary ONEhad been Written a large number of times into the same memory element bythe conventional method. The written-in region was then subsequentlysubjected to disturbance a large number of times by information pulsesfor ONEs, each having the same amplitude as that of the informationpulse used to write the binary ZERO.

Curve 17' shows the relationship between readout signal voltage leveland information pulse amplitude current of a memory element after it hasbeen subjected to the following processes:

CASE NO. 2

A binary ONE was written into the memory element once by theconventional writing method subsequent to the time in which a binaryZERO had previously been written a large number of times by the use ofthe conventional method. Then the written-in region was disturbed alarge number of times by many information pulses for ONEs, each havingthe same current amplitude as that of the information pulse used forwriting the binary ONE.

Curve 18 shows the relationship between readout signal level andinformation pulse amplitude of a memory element after it has beensubjected to a process similar to that detailed in Case No. 1 using theimproved writing method in place of the conventional writing method.

Curve 18 shows the relationship between readout signal level andinformation pulse amplitude current of a memory element after it hasbeen subjected to a process similar to that detailed in the abovementioned Case No. 2 wherein the improved writing method has beensubstituted for the conventional writing method.

Operating conditions under which the above experi- 6 ments wereperformed with the memory plane were as follows:

Word pulse amplitude 0.6 amp. Word pulse duration 0.15 ,usec. Auxiliarypulse amplitude 0.6 amp. Auxiliary pulse duration 0.06 ,usec.

Numerical values obtained by this experiment are listed in Table l.

Readout signal level in Readout signal level in mV. taken under simmV.taken under similar situations as menilar situations as mentioned inCase No. 1 tioned in Case No. 2

When the When the Information improved When the improved When the PulseAmpliwriting conventional writing convent onal tude, mA. method writingmethod writing was used, method was was used, method was 111 used, mV.mV. used, mV.

-18.0 19. 5 +19. 5 +19. 0 +3.0 12. 5 3. 0 +7. 8 +8v 3 8. 8 5. 5 +4. 0+11.0 +2. 5 7.7 5.0 +11.8 +7.0 8.0 7.5 +13. 0 +12. 0 ll. 0 10.0 +14.()+13. 0 12.0 --11. 0 +15. 0 +13. 8 -12. 5 1. 7 +15. 5 +14. 8 13. 0 --12.0+15. 5 +15. 6 -l4. 0 -13.0 +17. 0 +16. 0 14.0 13.0 +17. 0 17.0 14. 514.0 18. 8 -17. 8 19. 5 +18. 0

It should be evident that a memory element into which a binary ZERO (orbinary ONE) was written a large number of times and then subsequentthereto a binary ONE (or binary ZERO) was written once represents theWorst condition which can occur within a memory element because themargin of the information pulse becomes minimum under this conditionirrespective of the type of writing method employed.

Thus, by considering the operating characteristics of a memory elementunder the worst conditions, it goes without saying that the operatingconditions other than the Worst conditions need not be taken intoconsideration since such other operating conditions will always yieldbetter output results for a given driving condition.

As will be readily understood from the foregoing explantation, theorigin of information pulse amplitudes which are permissible for use inoperating a plated wire memory device are substantially increasedthrough the use of the improved writing methods set forth herein, and,accordingly, the margins of the word pulses can likewise be greatlyincreased to a certain extent corresponding to the increases ininformation pulses.

Since the storage capacity and hence the reliability of plated wirememory devices are vastly improved through the writing method describedherein, the successful yields of memory elements produced in themanufacturing process are appreciably raised, thus affording the writingmethod of the instant invention a great deal of practical utility.

Whereas the exemplary embodiment of the instant invention has beenassumed to employ a pulse timing diagram such as that shown in FIGURE 2wherein an information pulse is shown to be a continuous single pulse,it should be likewise understood that two separate information pulsesarranged in whatever manner may be introduced in lieu of a singlecontinuous pulse so long as the two information pulses conform to thetiming relationships set forth below:

A first information pulse should be initiated before the cessation ofthe regular word pulse and be terminated during the time intervalbetween the cessation of the regular word pulse and the initiation orcommencement of the auxiliary word pulse. The second information wordpulse should be initiated before the commencement or cessation of theauxiliary word pulse and be sustained for some time interval after thecessation or termination of the auxiliary word pulse.

It will be apparent from the foregoing explanation that the effect ofthe improved Writing method according to the instant invention remainsthe same in the particular arrangement set forth above.

The means employed to produce the information pulse into substrate wire1 may be any conventional means employed to operate plated wire memorydevices. The means employed to produce the regular word pulse andauxiliary word pulse may be any conventional means available in theelectronic art which is capable simply of producing two consecutivepulses opposite in polarity and substantially but not absolutely equalin amplitude. The information pulse generator 20, shown in FIG- URE 1,may be any suitable square pulse generating means such as, for example,a one-shot multivibrator. The word pulse generator 21 may, for example,be a one-shot multivibrator producing a substantially square pulse andhaving a differentiation circuit coupled to the output thereof so as toproduce successive positive and negative going pulses obtained throughdifferentiation of a single positive going pulse. The above choicesshould be considered as being merely exemplary and any other suitableelectronic circuits may be employed, depending only upon the needs ofthe user. Such suitable pulsing and digital techniques are set forth inmany engineering texts such as, for example, Pulse and Digital CircuitTechniques by Millman and Taub, copyright 1957 by McGraw-Hill.

Although this invention has been described with respect to its preferredembodiments, it should be understood that many variations andmodifications will now be obvious to those skilled in the art, and it ispreferred, therefore, that the scope of the invention be limited not bythe specific disclosure herein but only by the appended claims.

What is claimed is:

1. A method for writing binary information into a plated wire magneticfilm memory device comprised of a plurality of spaced parallelcylindrical magnetic film memory elements, each consisting of aconducting substrate wire, a thin magnetic film continuouslyelectroplated thereon and having an easy axis of magnetization in thecircumferential direction of said conducting substrate wire, and aplurality of spaced parallel solenoidform word drive lines disposedaround each of the plated wire substrates so as to be substantiallyperpendicularly aligned to said plated wires, characterized in that thebinary information states ONE and ZERO are written into said memory bysequentially introducing regular and auxiliary word pulses in said wordline and an information pulse in said conducting substrate wire so as tomeet the following timing relations:

(a) a regular word pulse followed by an auxiliary word pulse opposite inpolarity to said regular word pulse is selectively introduced into saidword drive lines;

(b) an information pulse is selectively introduced into said substratewires substantially before the cessation of the regular word pulse andis terminated after the cessation of the regular word pulse;

(0) and the auxiliary word pulse which is opposite in polarity to theregular word pulse is introduced in the time interval between thecessation of the regular word pulse and the cessation of the informationpulse.

2. The method of claim 1 wherein the step of introducing the regularword pulse is further comprised of producing a word pulse of positivepolarity.

3. The method of claim 2 wherein the step of producing an auxiliary wordpulse is further comprised of producing a word pulse which is ofnegative polarity.

4. The method of claim 3 wherein said regular and auxiliary word pulsesare opposite in polarity and of substantially equal amplitude.

5. A plated wire magnetic film memory comprising:

a plurality of spaced parallel cylindrical magnetic film memoryelements, each consisting of a conducting substrate wire, a thinmagnetic film continuously electroplated thereon and having an easy axisof magnetization in the circumferential direction of said conductingsubstrate wires;

a second set of spaced parallel solenoid-form word drive lines disposedaround each of the plated wire substrates so as to form one turntherearound, wherein said set of word drive lines are alignedsubstantially perpendicularly to said substrate wires;

first means for selectively generating an information current pulse insaid substrate wires;

second means for selectively introducing a regular word pulse currentfollowed by an auxiliary word pulse current in said word drive lines;

said second means being comprised of means for generating a positivegoing regular word pulse followed by a negative going auxiliary wordpulse with the timing relationships among the pulses being such that theinformation pulse in initiated before the termination of the regularword pulse and is terminated after the termination of the regular wordpulse, and the auxiliary word pulse is initiated in the time intervalbetween the termination of the regular word pulse and the termination ofthe information pulse.

References Cited Bittmann, E. E.: Thin Film Memories, InternationalSolid-State Circuits Conference, Feb. 12, 1959; pp. 22- 23.

BERNARD KONICK, Primary Examiner G. M. HOFFMAN, Assistant Examiner

